1. Field of the Invention
The invention relates to a motor rotor provided with a plurality of segment magnets fixed on the lateral surface of a rotor yoke, an electric power steering apparatus using the motor as a drive source thereof, and a method for producing the motor rotor.
2. Description of the Related Art
An example of this type of motor rotor is available in which a plurality of segment magnets are fixed with an adhesive to the outer peripheral surface of a rotor yoke having a cylindrical shape (see, for example, Japanese Patent Application Publication No. 2003-230239 (JP-A-2003-230239)).
However, since the coefficients of thermal expansion differ between the rotor yoke and the segment magnets, the adhesive is subjected to stress when the motor generates heat. When there are frequent opportunities for the motor being used at a high load and reaching a high temperature, the adhesive undergoes thermal deterioration resulting in a decrease in adhesive strength thereof. In addition, the adhesive strength of the adhesive similarly decreases in cases of being exposed to high temperatures and high-temperature environments for prolonged periods of time. Consequently, in the case segment magnets are fixed to a rotor yoke with an adhesive alone as in the structure of the related art, there is the possibility of the segment magnets separating from the rotor yoke and the output torque of the motor becoming unstable. When this type of motor is used in an electric power steering apparatus, the situation can occur in which steering feel decreases together with the decrease in output torque of the motor.